The following information is returned to the task by the I/O manager, in the I/O request table: The condition code for the SIO issued for the I/O operation The compcsite esw The SENSE tytes returned by the operation (if any) Using the information in this table, the I/O manager enqueues the
request on the specified subchannel, starts the I/O operation, assembles the return information in the requestor's I/O request table, and posts
the synchronization lock in the I/O request tatle signalling that the I/O operation is comFlete. Interruption Handling Supervisor service routines handle three kinds of interruptions:
external interruptions, sve interruptions, and I/O interruptions.
In RSeS, supervisor routines use the SVC (SUPERVISOR CALL) to suspend
the execution or dispatching of a task when that supervisor routine
received control. On an SVC interruption in RSCS, tMTSve is entered. DMTSVC saves the status of the executing task and passes control to the
calling sUFervisor rcutine in supervisor execution mode. RSCS handles external interruptions fro. tasks by searching fer
asynchronous exit requQsts supplied by tasks. When a request with a
code matching the external interruption code is found, its asynchronous exit is taken; otherwise, the external interruption is ignored. I/O interruptions are handled by the Rses I/O manager. When an
active IIO request causes an I/O interruption, the status of tbe I/C request is updated to reflect the new information. Otherwise, a search
is made for an asynchronous exit request for the interrupting device. When one is found, the asynchronous exit is taken. Otherwise, tbe
interruption is ignored. Virtual Storage Management
The supervisor virtual storage service routine IftTSTO bandIes requests
ty tasks fer main When a task requests main storage, DftTSiC reserves page(s) of storage for it. Main storage is freed directly by
task programs.
DMTQRQ manages requests for free
queue. SUFervisor routines call
supervisor status queue elements.
clements of the supervisor status DftTQRQ to reserve and release 3-10 IBM VM/370: System Logic and Problem Determination--Volume 3
RSCS Task Structure
As described in the previous section, the RSCS,supervisor comprises a
set of routines that function together to manage RSCS system processing.
The supervisor provides a base for many system programs called tasks.
(These tasks are not to be confused with user-application programs.)
The RSCS system service tasks perform less generalized functions fer
the system than those functions performed by the supervisor. Fer
example, the AIS system service task is designed specifically to access
the VM/370 spool file system.
The supervisor identically manages all tasks in RSCS; the superviser makeS no distinction between system service tasks and line driver tasks.
Figure 4 is a list of the Rses tasks and a trief statement of the
service each Ferforms. r
Handles console I/O; accepts requests for services
passed by other system service tasks line
driver tasks; terminates a task; handled program
check interruptions.
Creates a system service or line driver task.
Monitors processing of commands in RSCS; executes
Builds a message element and passes the element
to the appropriate tasks for transmission or
printing. Performs cosmon task functions.
communicates with the spool file system. Manages telecommunications line allocation.
Manages a telecommunications line for a
programmable reaote station using RTAM. Manages a telecommunications line for a remote station terminal. L- __________ __________________________________________________________ _
Figure 4. RSeS Tasks
CREATE SYSTEM TASKS: DMTCRE The main system service task, REX, is loaded with the supervisor during RSCS initialization. The REX task, in turn, creates other tasks
required by the system. DMTCRE reads these other tasks fro. a CMS disk ty. means of a CMS read access method. The task is then started as a new active task under RSCS. Introduction 3-11
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